Vulnerability · Published Mar 20, 2026 · Assigned by GitHub_M

CVE-2026-32887Effect Bug: `AsyncLocalStorage` context lost/contaminated inside Effect fibers under concurrent load with RPC

High 7.4

In plain English

A high-severity race condition in effect from Effect-TS. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 21% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.4High

Exploit odds (30 days)0.3%top 78.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

Effect is a TypeScript framework that consists of several packages that work together to help build TypeScript applications. Prior to version 3.20.0, when using `RpcServer.toWebHandler` (or `HttpApp.toWebHandlerRuntime`) inside a Next.js App Router route handler, any Node.js `AsyncLocalStorage`-dependent API called from within an Effect fiber can read another concurrent request's context — or no context at all. Under production traffic, `auth()` from `@clerk/nextjs/server` returns a different user's session. Version 3.20.0 contains a fix for the issue.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	effect	3.20.0	GHSA-38f7-945m-qr2g

Affected products (as reported)

Vendor	Product	Versions
Effect-TS	effect	< 3.20.0

Weakness: CWE-362 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

References

https://github.com/Effect-TS/effect/security/advisories/GHSA-38f7-945m-qr2g x_refsource_CONFIRM